Interesting article. Well written and gives one something to think about. I have coolers on both of my bikes. Put it on the ultra myself with first oil change along with an oil temp gauge and the xl came with one installed by previous owner. I didn't need one on the ultra as it is stock, but I plan to do some mods and would rather have one once I am putting out some more power. My xl is a 4 5/8 stroke and it is bored .040 over with dual plugs and 10.5:1 compression and a wild cam. I would not run the xl without one as the oil is rarely cooler than 220F within 20 minutes of running.
Are the coolers really needed? All just opinion I guess, what you want, can afford etc..... I feel much better having the oil cooler on both bikes and for the $400 it cost me to put it on the ultra, it is a small price to pay for piece of mind.
For what it is worth, I drive a Cadillac and it has (rather large) coolers for the oil, transmission, and power steering.

The internet has provided a platform for anyone that has an opinion to speak out so to say.

Been around motorcycles since I was 15 years old. Been working on motors a couple of years more. The most common killer of any engine is heat.

As an air cooled engine the Harley has to rely on air movement over the case and fins for "Max" cooling. Even when your sitting still the fins are still radiating heat. Ask the people with "fried thighs."

With the change of the motor to include a piston spray Harley reduced the piston heat by about 50º. But this did add a temperature rise in the oil. Add the change to fuel injection and the epa requirements and we have more heat.

I'm old school in that I believe you need to know what your engine is doing. I added oil temp and oil pressure gauges on my 2006 Low Rider and on my current ride a 2007 Heritage. I can tell you that my TC88 and TC96 requires a 25 to 30 minute ride in 75º outside temp to bring the oil up to an operating temp of 220º.

In ambient temps of 100º the oil in the TC88 of the FXDLI and the TC96 of the FLSTC would borderline on 260º rising to 280º+ if required to idle in traffic for extended periods. This is not good even with me running synthetic in both rides.

I added a billet style oil cooler by wimmer with a Jagg oil takeoff adapter (thermostat controlled) to my Low Rider to get control of the temps in the extreme heat. I mounted the oil cooler horizontally just below the regulator. I had an overal reduction of approximately 20º at idle to 25º at normal rpm. Yes even at idle a oil cooler radiates heat. I have not put one on my Heritage yet but it is sitting in the toolbox ready to go.

The oil pressure of the TC88 and TC96 ran 30 to 35psi at 3000 rpm and would drop to 5 to 9 psi at idle. With the addition of the cooler I saw no noticeable pressure drop on the Low Rider or the Heritage. I have not performed a flow test but I would not expect the cooler to reduce the flow much at all.

Jagg specs for their 10 row cooler is shown below. Taken from their site.

I can tell you from personal experience his fear of pressure drops and gushing oil leaks (I do know how to tighten a fitting) is without merit.

Oil coolers do the job they were intended for. By using a temp controlled takeoff you will not risk the chance of lowering the oil temp below operating standards.

Tips for the Oil Cooler installation:

Use a temperature controlled bypass. Oil will not go through the cooler until it bypasses. The Jagg 4700 starts at 185º and is fully open by 195º. You will not run your oil "too cool".

Use fittings designed for flow not show. The wimmer cooler came with 3/8" hose fittings that had a huge id. You can see the size of the hole on their page. (link above)

Use good hose and clamps. And for heaven sake just tighten the dang things.

With the advent of temperature controlled bypass valve design, the odds of over cooling are gone. The other thing is modern engines get up to temperature quickly BECAUSE fuel injection and ignition being electronically controlled for lean "best" running means you do not run rich or raw fuel contributed over cooling or flooding issues.

He also talked about being stopped in traffic the oil cooler does not work...untrue...heat conduction is still occurring because of turbulator vanes within the tubes engage more surface area within, the oil swirling within transfers more heat to the outside fins, while getting convection cooling (heated air rises, even without the directional breeze), carrying heat away. Since the delta between inner oil is say 250*F and outside air is 100*F there is 150*F difference, that heat is being transferred to the colder air, be it at cooler or the finned heads nonetheless...

This means with the valve, you do not have to "cover" the cooler from air blowing over it (remember us doing that on radiator equipped cars for fear of freezing in snow bound days? So don't let the "hear say evidence sway you" from putting a cooler on...especially if you live in a temperate area or experiencing rear cylinder protect mode in moderately hot weather. As been said before..."--your ride, you decide"!